Calculate lift for every row and compare it with the average lift of region and year

I have a table that looks like the one below:

So far I have calculated the columns Shop, Year, Region, Waste, Avg Waste (Year, Region), Lift. I want to calculate the one marked as Column_I_want_To_Calculate.

Briefly, it computes the average lift per Region and Year and compares Shops' Lift with the Average Lift of all shops in the same Region and Year. Then assigns the value 1 or 0 in case of a greater than statement.

So far I have tried (PostgreSQL),

SELECT  shop
        ,year
        ,region
        ,waste
        ,AVG(waste) over (partition by year, region) as "Avg Waste (Year,Region)"
        ,waste/avg(waste) over (partition by year, region) AS Lift,
        ,CASE WHEN waste/avg(waste) over (partition by year, region) > 
           (SELECT tab2.avg_lift 
            FROM (
              SELECT tab1.year, tab1.region, AVG(tab1.lift) OVER (PARTITION BY tab1.year, tab1.region) avg_lift
              FROM (
                  SELECT year, region, waste/ avg(waste) over (partition by year, region) AS lift
                  FROM main_table
                  GROUP BY year,region,waste
                  ORDER BY lift DESC
              ) tab1
              GROUP BY tab1.year, tab1.region, tab1.lift
           ) tab2
        ) THEN 1 ELSE 0 END AS "Column_I_want_To_Calculate"
FROM main_table
GROUP BY shop,
         year,
         nomos,
         waste
;

However, the code above throws the exception

postgresql error: more than one row returned by a subquery used as an expression

This one returns the required output based on your input:

SELECT  
        region
    ,   shop
    ,   waste
    ,   round(AVG(waste) OVER w,2) AS avg_waste
    ,   round(waste / AVG(waste) OVER w,2) AS lift
    ,   CASE
            WHEN waste > AVG(waste) OVER w THEN 1
            ELSE 0
        END AS above_average
FROM    i
WINDOW  w AS (PARTITION BY year, region)
ORDER BY
    1,2,3;